The present invention relates in particular to the field of computer-assisted navigation in surgery (IGS or “image-guided surgery”). Within this field, it is necessary to detect the spatial location of the bones using a surgical navigation system. A surgical navigation system and/or navigation system is understood to mean a system which consists of at least one marker device, a transmitter which emits electromagnetic waves and/or radiation and/or ultrasound waves, and a receiver which receives electromagnetic waves and/or radiation and/or ultrasound waves, as well as an electronic data processing device which is connected to the receiver and/or the transmitter, wherein the data processing device (for example, a computer) comprises a processor (CPU), a working memory, advantageously an indicating means (for example, a visual indicating means such as a monitor and/or an audio indicating means such as a loudspeaker) and advantageously a permanent data memory, wherein the data processing device processes navigation data relayed to it from the receiver and can advantageously output guidance information to a user via the indicating means. The navigation data can be stored in the permanent data memory and for example compared with data which has been provided in said memory beforehand. In order to detect the location of the bones, landmarks on the bone are for example tapped by means of a pointer, so as to communicate the location of the landmark to the navigation system, so as to be able to produce a three-dimensional image of the bone which shows the position of the bone. In short, the bone is registered with the aid of the navigation system. A pointer is a tool, in particular a rod, with a number of markers—advantageously, three markers—fastened to it, wherein the relative location between the markers and the tip of the pointer is known. Thus, by detecting the position of the markers, it is possible to determine where the tip of the pointer is situated. If the tip of the pointer is brought into contact with a landmark, the position of the landmark of the bone is thus known.
It is the function of a marker to be detected by a marker detection device (a detection device such as for example a camera or an ultrasound receiver) of the navigation system, such that its spatial position (i.e. location and/or alignment) can be ascertained. Such markers can be active markers. An active marker emits for example electromagnetic radiation and/or waves, wherein said radiation can be in the infrared, visible and/or ultraviolet spectral range. The marker can also however be passive, i.e. can for example reflect electromagnetic radiation from the infrared, visible and/or ultraviolet spectral range. To this end, the marker can be provided with a surface which has corresponding reflective properties. It is also possible for a marker to reflect and/or emit electromagnetic radiation and/or waves in the radio frequency range or at ultrasound wavelengths. A marker preferably has a spherical and/or spheroid shape and can therefore be referred to as a marker sphere; markers can however also exhibit a cornered—for example, cubic—shape.
A “reference star” refers to a device with a number of markers, advantageously three markers, attached to it, wherein the markers are attached to the reference star such that they are stationary and advantageously detachable, thus providing a known (and advantageously fixed) position of the markers relative to each other. The position of the markers relative to each other can be individually different for each reference star used within the framework of a surgical navigation method, in order to enable the corresponding reference star to be identified by a surgical navigation system on the basis of the position of the markers relative to each other. It is therefore also then possible for the objects (for example, instruments and/or parts of a body) to which the reference star is attached to be identified and/or differentiated from each other. In a surgical navigation method, the reference star serves to attach a plurality of markers to an object (for example, a bone or a medical instrument) in order to be able to detect the spatial position of the object (i.e. its location and/or alignment). Such a reference star in particular comprises a way of being attached to the object (for example, a clamp and/or a thread) and/or a holding element which ensures a distance between the markers and the object (in particular in order to assist the visibility of the markers to a marker detection device) and/or marker holders which are mechanically connected to the holding element and which the markers can be attached to. Where it is clear from the context, the term “reference star” can also refer to a reference star with at least one marker attached to it. Such a system consisting of a reference star and at least one marker can also be referred to as a marker star.
A marker device comprises at least one marker, preferably at least two or three markers, and can for example be a reference star, a pointer and/or an individual marker or a number of markers. A marker device which is attached (such that it is stationary) to the tool is also referred to here as a tool marker device. A marker device which is attached (such that it is stationary) to the body structure is also referred to here as a body structure marker device.
Detecting landmarks by means of pointers is time-consuming and extends the operation time and thus the burden on the patient.
When resecting the distal end of the femur in order to replace it with an implant, particular variable information about the distal end of the femur is required. This information is conventionally captured in such a way that a pointer is moved to the condyles in order to detect the most distal point in each case. A corresponding procedure is followed in order to detect the furthest posterior point on the posterior side of each of the condyles. This procedure is time-consuming.